System and method for providing surgical instrument force feedback

ABSTRACT

Embodiments of an actuated cannula seal are disclosed In some embodiments, a cannula seal includes a base portion that engages with a cannula; and a seal portion integrally formed with the base portion, the sealing portion capable of engaging with an instrument shaft, the sealing portion capable of being actuated by an actuator so that the sealing portion is continually in motion relative to the instrument shaft. The actuation of the sealing portion can be accomplished by rotation or vibration of the sealing portion relative to the instrument shaft.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityunder 35 U.S.C. § 120 to U.S. patent application Ser. No. 15/992,030,filed on May 29, 2018, which is a continuation of and claims the benefitof priority under 35 U.S.C. § 120 to U.S. patent application Ser. No.15/411,527, filed on Jan. 20, 2017, which is a continuation of andclaims the benefit of priority under 35 U.S.C. § 120 to U.S. patentapplication Ser. No. 14/181,541, filed on Feb. 14, 2014, which claimsthe benefit of priority under 35 U.S.C. § 119(e) to U.S. PatentApplication Ser. No. 61/765,616, filed on Feb. 15, 2013, each which isherein incorporated by reference herein in its entirety.

TECHNICAL FIELD

Embodiments of the present invention are related to seals, and inparticular to cannula seals for minimally invasive robotic surgery.

DISCUSSION OF RELATED ART

Surgical procedures can be performed through a surgical robot in aminimally invasive manner. The benefits of a minimally invasive surgeryare well known and include less patient trauma, less blood loss, andfaster recovery times when compared to traditional, open incisionsurgery. In addition, the use of robot surgical systems (e.g.,teleoperated robotic systems that provide telepresence), such as the daVinci® Surgical System manufacture by Intuitive Surgical, Inc. ofSunnyvale, Calif., is known. Such teleoperated surgical systems mayallow a surgeon to operate with intuitive control and increasedprecision when compared to manual minimally invasive surgeries.

In a minimally invasive surgical system, surgery is performed by asurgeon controlling the teleoperated robot. The robot includes one ormore instruments that are coupled to arms. The instruments access thesurgical area through small incisions through the skin of the patient. Acannula is inserted into the incision and a shaft of the instrument canbe inserted through the cannula to access the surgical area. A sealbetween the cannula and the instrument shaft allows the incision to besealed during the surgery. Existing cannula seals may have excessive,variable and direction dependent friction that can interfere with finepositioning and force sensing of the instrument tip in theinsertion-retraction direction as it contacts surgical patient anatomy.

Therefore, there is a need to develop better performing cannula sealsfor minimum invasive surgical systems.

SUMMARY

In accordance with aspects of the present invention an actuated cannulaseal and a system using the actuated cannula seal is presented. In someembodiments, a cannula seal includes a base portion that engages with acannula; and a seal portion integrally formed with the base portion, thesealing portion capable of engaging with an instrument shaft, thesealing portion capable of being actuated by an actuator so that thesealing portion is continually in motion relative to the instrumentshaft. The actuation of the sealing portion can be accomplished byrotation or vibration of the sealing portion relative to the instrumentshaft.

A method of providing haptic feedback for motion along an instrumentshaft according to some embodiments of the present invention can includeactuating a cannula seal such that a sealing portion of the cannula sealis in motion with respect to the instrument shaft; measuring a forcealong the instrument shaft; correcting the measured force for modeledcannula seal friction; and transmitting the corrected force data tocontrols operated by a surgeon.

A system according to some embodiments of the present invention includesan actuated cannula seal that seals between a cannula and a surgicalinstrument; force sensors coupled to the surgical instrument, the forcesensors sensing force along an axis of the surgical instrument; and afeedback system that receives force data from the force sensors andcorrected the force data according to modeled cannula seal friction toform corrected force data.

These and other embodiments are further discussed below with respect tothe following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 1C illustrate components of an example teleoperatedrobotic surgical system.

FIG. 2 illustrates cannulas as utilized by the system of FIGS. 1A, 1B,and 1C.

FIGS. 3A and 3B illustrate operation of a haptic feedback systemaccording to some embodiments of the present invention.

FIGS. 4A and 4B illustrate a cannula seal.

FIGS. 5A and 5B illustrate force models that can be utilized in someembodiments of the present invention.

FIGS. 6A, 6B ad 6C illustrate an actuated cannula seal according to someembodiments of the present invention.

FIG. 7A illustrates an actuated cannula seal with a piezoelectricactuator according to some embodiments of the present invention.

FIG. 7B illustrates an actuated cannula seal with a voice coil actuatoraccording to some embodiments of the present invention.

FIGS. 8A, 8B, and 8C illustrate some example embodiments ofpiezoelectric actuators that can be used in the actuated cannula sealillustrated in FIG. 7A.

FIGS. 9A and 9B illustrate an actuated seal with a pneumatic actuatoraccording to some embodiments of the present invention.

DETAILED DESCRIPTION

In the following description, specific details are set forth describingsome embodiments of the present invention. It will be apparent, however,to one skilled in the art that some embodiments may be practiced withoutsome or all of these specific details. The specific embodimentsdisclosed herein are meant to be illustrative but not limiting. Oneskilled in the art may realize other elements that, although notspecifically described here, are within the scope and the spirit of thisdisclosure.

This description and the accompanying drawings that illustrate inventiveaspects and embodiments should not be taken as limiting—the claimsdefine the protected invention. Various mechanical, compositional,structural, and operational changes may be made without departing fromthe spirit and scope of this description and the claims. In someinstances, well-known structures and techniques have not been shown ordescribed in detail in order not to obscure the invention.

Additionally, the drawings are not to scale. Relative sizes ofcomponents are for illustrative purposes only and do not reflect theactual sizes that may occur in any actual embodiment of the invention.Like numbers in two or more figures represent the same or similarelements.

Further, this description's terminology is not intended to limit theinvention. For example, spatially relative terms—such as “beneath”,“below”, “lower”, “above”, “upper”, “proximal”, “distal”, and thelike—may be used to describe one element's or feature's relationship toanother element or feature as illustrated in the figures. Thesespatially relative terms are intended to encompass different positions(i.e., locations) and orientations (i.e., rotational placements) of adevice in use or operation in addition to the position and orientationshown in the figures. For example, if a device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be “above” or “over” the other elements or features.Thus, the exemplary term “below” can encompass both positions andorientations of above and below. A device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly. Likewise, descriptionsof movement along and around various axes include various special devicepositions and orientations. In addition, the singular forms “a”, “an”,and “the” are intended to include the plural forms as well, unless thecontext indicates otherwise. And, the terms “comprises”, “comprising”,“includes”, and the like specify the presence of stated features, steps,operations, elements, and/or components but do not preclude the presenceor addition of one or more other features, steps, operations, elements,components, and/or groups. Components described as coupled may beelectrically or mechanically directly coupled, or they may be indirectlycoupled via one or more intermediate components.

Elements and their associated aspects that are described in detail withreference to one embodiment may, whenever practical, be included inother embodiments in which they are not specifically shown or described.For example, if an element is described in detail with reference to oneembodiment and is not described with reference to a second embodiment,the element may nevertheless be claimed as included in the secondembodiment.

Aspects of embodiments of the invention are described within the contextof a particular system. Knowledgeable persons will understand, however,that inventive aspects disclosed herein may be embodied and implementedin various ways, including robotic and non-robotic embodiments andimplementations. Implementations described herein are merely exemplaryand are not to be considered as limiting the scope of the inventiveaspects disclosed herein. In particular, some embodiments of theinvention assist in better force calculations along a surgicalinstrument in order to provide force information to the surgeoncontrolling the surgical robot.

FIGS. 1A, 1B, and 1C are front elevation views of three main componentsof a teleoperated robotic surgical system for minimally invasivesurgery. These three components are interconnected so as to allow asurgeon, with the assistance of a surgical team, to perform diagnosticand corrective surgical procedures on a patient.

FIG. 1A is a front elevation view of the patient side cart component 100of a surgical system. The patient side cart includes a base 102 thatrests on the floor, a support tower 104 that is mounted on the base 102,and several arms that support surgical tools. As shown in FIG. 1A, arms106 a, 106 b, and 106 c are instrument arms that support and move thesurgical instruments used to manipulate tissue. Arm 108, for example,can be a camera arm that supports and moves an endoscope instrument 112.Instrument arm 106 c can be an optional third instrument arm 106 c thatis supported on the back side of support tower 104 and that can bepositioned to either the left or right side of the patient side cart asnecessary to conduct a surgical procedure. FIG. 1A further showsinterchangeable surgical instruments 110 a,110 b,110 c mounted on theinstrument arms 106 a,106 b,106 c, and it shows endoscope 112 mounted onthe camera arm 108. Knowledgeable persons will appreciate that the armsthat support the instruments and the camera may also be supported by abase platform (fixed or moveable) mounted to a ceiling or wall, or insome instances to another piece of equipment in the operating room(e.g., the operating table). Likewise, they will appreciate that two ormore separate bases may be used (e.g., one base supporting each arm).

As is further illustrated in FIG. 1A, instruments 110 a, 110 b, 110 c,and endoscope 112 include an instrument interface 150 a, 150 b, 150 c,and 150 d, respectively, and an instrument shaft 152 a, 152 b, 152 c,and 152 d, respectively. In some embodiments, component 100 can includesupports for cannulas that fix instruments 110 a, 110 b, 110 c, andendoscope 112 with respect to the cannulas.

Further, portions of each of the instrument arms 106 a, 106 b, and 106 care adjustable by personnel in the operating room in order to positioninstruments 110 a, 110 b, and 110 c with respect to a patient. Otherportions of arms 106 a, 106 b, and 106 c are actuated and controlled bythe surgeon at a surgeon's console 120. Surgical instruments 110 a, 110b, 110 c, and endoscope 112, can also be controlled by the surgeon atsurgeon's console 120.

FIG. 1B is a front elevation view of a surgeon's console 120 componentof a surgical system. The surgeon's console 120 is equipped with leftand right multiple degrees of freedom (DOF) master tool manipulators(MTM's) 122 a, 122 b, which are kinematic chains that are used tocontrol the surgical tools. The surgeon grasps a pincher assembly 124 a,124 b on each MTM 122, typically with the thumb and forefinger, and canmove the pincher assembly to various positions and orientations. When atool control mode is selected, each MTM 122 is coupled to control acorresponding instrument arm 106 for the patient side cart 100. Forexample, left MTM 122 a may be coupled to control instrument arm 106 band instrument 110 a, and right MTM 122 b may be coupled to controlinstrument arm 106 b and instrument 110 b. If the third instrument arm106 c is used during a surgical procedure and is positioned on the leftside, then left MTM 122 a can be switched between controlling arm 106 aand instrument 110 a to controlling arm 106 c and instrument 110 c.Likewise, if the third instrument arm 106 c is used during a surgicalprocedure and is positioned on the right side, then right MTM 122 a canbe switched between controlling arm 106 b and instrument 110 b tocontrolling arm 106 c and instrument 110 c. In some instances, controlassignments between MTM's 122 a, 122 b and arm 106 a/instrument 110 acombination and arm 106 b/instrument 110 b combination may also beexchanged. This may be done, for example, if the endoscope is rolled 180degrees, so that the instrument moving in the endoscope's field of viewappears to be on the same side as the MTM the surgeon is moving. Thepincher assembly is typically used to operate a jawed surgical endeffector (e.g., scissors, grasping retractor, needle driver, and thelike) at the distal end of an instrument 110.

In accordance with certain aspects of the present invention, MTM's 122a, 122 b can provide haptic force feedback to the surgeon. This forcefeedback allows the surgeon to more accurately control the MTM's so asto operate the jawed surgical end effectors of instruments 110 a, 110 band 110 c. Accurate sensing of forces on instruments 110 a, 110 b and110 c allows for a reliable force feedback, which allows the surgeon tomore accurately control instruments 110 a, 110 b and 110 c.

Surgeon's console 120 also includes a stereoscopic image display system126. Left side and right side images captured by the stereoscopicendoscope 112 are output on corresponding left and right displays, whichthe surgeon perceives as a three-dimensional image on display system126. In an advantageous configuration, the MTM's 122 are positionedbelow display system 126 so that the images of the surgical tools shownin the display appear to be co-located with the surgeon's hands belowthe display. This feature allows the surgeon to intuitively control thevarious surgical tools in the three-dimensional display as if watchingthe hands directly. Accordingly, the MTM servo control of the associatedinstrument arm and instrument is based on the endoscopic image referenceframe. In accordance with certain aspects of the present invention, thestereoscopic image display 126 can also be used to visually displayforce feedback to the surgeon (e.g. a number corresponding to themagnitude of the applied force).

The endoscopic image reference frame is also used if the MTM's 122 areswitched to a camera control mode. If the camera control mode isselected, the surgeon may move the distal end of the endoscope by movingone or both of the MTM's 122 together (portions of the two MTM's 122 maybe servo-mechanically coupled so that the two MTM portions appear tomove together as a unit). The surgeon may then intuitively move (e.g.,pan, tilt, zoom) the displayed stereoscopic image by moving the MTM's122 as if holding the image in the hands.

The surgeon's console 120 is typically located in the same operatingroom as the patient side cart 100, although it is positioned so that thesurgeon operating the console is outside the sterile field. One or moreassistants typically assist the surgeon by working within the sterilesurgical field (e.g., to change tools on the patient side cart, toperform manual retraction, etc.). Accordingly, the surgeon operatesremote from the sterile field, and so the console may be located in aseparate room or building from the operating room. In someimplementations, two consoles 120 (either co-located or remote from oneanother) may be networked together so that two surgeons cansimultaneously view and control tools at the surgical site.

FIG. 1C is a front elevation view of a vision cart component 140 of asurgical system. The vision cart 140 houses the surgical system'scentral electronic data processing unit 142 and vision equipment 144.The central electronic data processing unit includes much of the dataprocessing used to operate the surgical system. In various otherimplementations, however, the electronic data processing may bedistributed in the surgeon console and patient side cart. The visionequipment includes camera control units for the left and right imagecapture functions of the stereoscopic endoscope 112. The visionequipment also includes illumination equipment (e.g., Xenon lamp) thatprovides illumination for imaging the surgical site. As shown in FIG.1C, the vision cart includes an optional 24-inch touch screen monitor146, which may be mounted elsewhere, such as on the patient side cart100. The vision cart 140 further includes space 148 for optionalauxiliary surgical equipment, such as electrosurgical units andinsufflators. The patient side cart and the surgeon's console arecoupled via optical fiber communications links to the vision cart sothat the three components together act as a single teleoperatedminimally invasive surgical system that provides an intuitivetelepresence for the surgeon. And, as mentioned above, a secondsurgeon's console may be included so that a second surgeon can, e.g.,proctor the first surgeon's work.

During a typical surgical procedure with the robotic surgical systemdescribed with reference to FIGS. 1A-IC, at least two incisions are madeinto the patient's body (usually with the use of a trocar to place theassociated cannula). One incision is for the endoscope camerainstrument, and the other incisions are for the surgical instruments. Insome surgical procedures, several instrument and/or camera ports areutilized to provide access and imaging for a surgical site. Although theincisions are relatively small in comparison to larger incisions usedfor traditional open surgery, a minimum number of incisions is desiredto further reduce patient trauma and for improved cosmesis.

FIG. 2 illustrates utilization of the surgical instrument illustrated inFIGS. 1A, 1B, and 1C. As shown in FIG. 2, shafts 152 a, 152 b, and 152 dpass through cannulas 202 a, 202 b, and 202 c, respectively. Cannulas202 a, 202 b, and 202 c extend through instrument incisions 204 a, 204b, and 204 c, respectively. End effectors 206 a, 206 b, and 206 c areattached to shafts 152 a, 152 b, and 152 d, respectively. As discussedabove, end effectors 206 a, and 206 b can be jawed surgical endeffectors (e.g., scissors, grasping retractor, needle driver, and thelike). Further, end effector 206 c is illustrated as an endoscope tip.As shown in FIG. 2, cannulas 202 a, 202 b, and 202 c and shafts 152 a,152 b, and 152 d are positioned so that end effectors 206 a, 206 b, and206 c operate in a surgical area 210.

As shown in FIG. 2 cannulas 202 a. 202 b, and 202 c include mountingfittings 208 a, 208 b, and 208 c, respectively, that can be engaged byarms 106 a, 106 b, and endoscope arm 108, respectively, to allow forvery little movement of the instrument end effectors 206 a, 206 b, and206 c, respectively, as possible. Cannulas 202 a, 202 b, and 202 cfurther include cannula seal mounts 212 a, 212 b, and 212 c,respectively.

Cannula seals mounted to cannula seal mounts 212 a, 212 b, and 212 cprevent leakage around shafts 152 a, 152 b, and 152 d, respectively.During surgery, particularly if the surgery is abdominal surgery,pressurized CO₂ can be utilized to expand the abdomen, allowing forbetter access to surgical area 210. Further, cannula seals attached tocannula seal mounts 212 a, 212 b, and 212 c prevent leakage of fluids orother materials from the patient.

During the operation, the surgeon sitting at surgeon's console 120 canmanipulate end effectors 206 a, 206 b, and 206 c as well as move shafts152 a, 152 b, and 152 d along force lines F_(a), F_(b), and F_(c),respectively. These force lines represent forces along theinsertion/retraction direction (i.e., the direction along shaft 152).Collectively, whether insertion or retraction, this direction may bereferred to as the insertion direction.

As shown in FIG. 3A, utilizing various force measuring devices 304, theforces measured on end effectors 206 a, 206 b, and 206 c can be used toprovide force feedback to the surgeon at console 120, usually throughresistance to the surgeon's input at MTMs 122, to allow the surgeon tocontrol the force applied to end effectors 206 a, 206 b, and 206 c andcan also be used to counter frictional forces by compensating drivers inpatient side cart 100.

FIG. 3A also illustrates a cannula seal 302 according to someembodiments of the present invention sealing shaft 152 and engagingcannula mount 212. As shown in FIG. 3A, force data is provided bymeasuring devices 304 to a haptic feedback system 316. Haptic feedbacksystem 316 processes the force data and provides haptic feedback data tosurgeon console 120. The haptic feedback data can be utilized to controlmotors and thus provide the resistance to the surgeon's input at MTMs122. Additionally, or in place of controlling the motors directly, thehaptic feedback data can be visually displayed to the surgeon on thesurgeon's 3D visual display 126. Additionally, feedback data can beprovided to patient side cart 100 to compensate instrument drivers.

Effective surgical instrument force feedback utilizes a full 3dimensional sensing of the forces at end effectors 206 (collectivelyreferring to end effectors 206 a, 206 b, and 206 c). While satisfactoryinstrument shaft mounted force transducers provide good feedback for thetransverse surgical forces applied to patient tissue through wrists andjaws of end effectors 206, wrist actuation cable forces utilized tooperate end effectors 206 may prevent accurate sensing of surgicalforces in the insertion direction (i.e., the direction along shafts 152(collectively referring to shafts 152 a, 152 b, 152 c, and 152 d)) atthe end effector. As a result, insertion direction forces are typicallysensed at the back of surgical instruments 110 (collectively referringto surgical instruments 110 a, 110 b, 110 c, and endoscope 112) atinstrument interface 150 (collectively referring to instrumentinterfaces 150 a, 150 b, 150 c, and 150 d) or on arm 106 (collectivelyreferring to arms 106 a, 106 b, and 106 c or endoscope 112). In thosecases, the frictional forces of shaft 152 sliding through cannula seals302 mounted to cannula seal mount 212 (collectively referring to cannulaseals mounts 212 a, 212 b, and 212 c) becomes important, especially ifthat frictional force varies with direction (insertion or retraction),or velocity of shaft 152 through seal 212. In the discussion below,unequal insertion direction forces will be referred to as asymmetricwhile equal insertion and retraction forces will be referred to assymmetric. Cannula seal features in sliding contact with an insertedinstrument shaft will also be referred to as symmetric when similarfeatures face in opposite directions along the insertion direction orwhen such features do not point either way. Some embodiments of seal 302according to the present invention substantially reduces or eliminatesthe static friction between seal 302 and instrument shaft 152, andtherefore allow for more accurate feedback of forces to the operatingsurgeon. In some embodiments, cannula seal 302 is actuated such thatseal 302 is in motion with respect to instrument shaft 152 at thecontact between instrument shaft 152 and seal 302.

FIG. 3B illustrates an algorithm for processing the force data fromforce sensor 304. In some embodiments, the algorithm illustrated in FIG.3B can be implemented in feedback system 316, which can be implementedby the surgeon's console 120. In some embodiments, the algorithmillustrated in FIG. 3B can be implemented in feedback system 316, whichcan be implemented by the patient side cart 100. In some embodiments,the algorithm illustrated in FIG. 3B can be implemented as visualfeedback to the surgeon on the surgeon's visual display system 126. Asshown in FIG. 3B, a force measurement is taken by force sensor 304 instep 310. In step 312, the force measurement is corrected for cannulaseal friction. In step 312, the cannula seal friction using a cannulaseal 302 according to some embodiments of the present invention can bepredictable. In some embodiments, the cannula seal friction can besymmetric with respect to insertion and retraction direction. In someembodiments, the cannula seal friction can be substantially zero. Instep 314, the corrected force can be used to provide haptic feedback tothe surgeon at console 122, for example by applying a resistance forceto the motion of a MTM 122. In step 315, the corrected force can bedisplaying to the surgeon on the 3D viewer. In step 317, the correctedforce can be used in the patient side cart 100 as an input to thecontroller for the patient side manipulator to compensate for themeasured resistive force.

Cannula seals have taken a number of forms including simpleunidirectional compliant lip seals, tri-cuspid or multi-cuspid radialleaf seals, and spirally stacked overlapping and/or folded seal leavesakin to a traditional camera lens iris. Each of these types of sealshave asymmetric construction which causes unequal seal frictional forcedepending on the direction of motion. Examples of seals that exhibitsymmetrical force modeling are described in U.S. Pat. App. Ser. No.61/599,288, which is herein incorporated by reference in its entirety.

FIGS. 4A and 4B illustrate a conventional cannula seal 402. As shown inFIG. 4A, cannula seal 402 includes a base portion 406 and a retainingportion 408. Base portion 406 is attachable to cannula 202 at cannulaseal mount 212 and is held in place by retaining portion 408, which isintegrally formed with base portion 406. Retaining portion 408 alsoprovides for sealing against cannula seal mount 212.

Further, cannula seal 402 includes a seal lip 404 that seals aroundshaft 152. FIG. 4B illustrates lip 404 sealing around shaft 152. As isillustrated in FIGS. 4A and 4B, lip 404 is asymmetric and is oriented inthe insertion direction. Thus, shaft 152 will experience a differentfrictional force based on direction of motion. As is illustrated in FIG.3B, lip 404 is oriented in a direction that facilitates motion of shaft152 in the insertion direction. However, in the retraction direction,friction with shaft 152 compresses lip 304 about shaft 152 causing amuch higher frictional force. In some cases, the ratio in force betweeninsertion and retraction of shaft 152 can be a factor of about 1.5.

In some cases, especially with abdominal surgery, the direction of lip404 assists in sealing against insufflation pressure. In abdominalsurgery, pressurized CO₂ is provided into the abdomen by an insufflationsystem in order to expand the abdomen. CO₂ utilized in the insufflationsystem is typically supplied by a pressurized CO₂ tank and a regulator.The CO₂ pressure in the abdomen will load lip 304 by providing a forcethat pushes lip 404 more firmly against shaft 152.

Some other cannula seals have two transversely opposing lips like ashortened version of an oboe reed. Yet other seals have a simplecompliant circular hole in a diaphragm. In this case, the deflectiondirection of the seal inverts, the result being that the seal lip facesin the direction opposite where it started, when motion of the shaftthrough the seal reverses direction, causing further uneven insertionfriction force effects. Still other designs rely on an open complianthole with a rigid plastic door that is pushed aside when the instrumentshaft passes through the seal. In this case, the hinge direction of thedoor exerts asymmetric direction dependent friction forces on theinstrument. In every case of existing seals, the forces are excessive,direction dependent, and vary too much with operating conditions topermit motion direction based subtraction of the expected frictionforces from sensed forces to null out the frictional effects. Theexpected friction force contribution may be based on experimentalmeasurements. Therefore, utilizing these seals, the frictional forceprovides for unreliable force feedback to the surgeon.

Other than the application of lubricant, this problem has not beenaddressed. Some manufacturers of laparoscopic cannula seals provide aseparately packaged pouch of lubricant such as silicone or purified(white mineral oil based) petroleum grease for optional use or pre-coatthe seal with such a grease. Silicone or other rubber materials utilizedas a seal have a relatively high dry coefficient of friction. Greaselubricants help but do not sufficiently reduce seal friction and maywipe off during a procedure so that the friction varies with time.Grease lubricants also do not equalize the direction dependent forcesdue to asymmetric seal lip design. Therefore, addition of lubricatingmaterials alone does not significantly help with the asymmetricfrictional forces applied when the instrument shaft is moved through aseal.

In some embodiments, the noise limited force sensitivity of a transverseinstrument force transducer allows measurement of forces significantlylower than the frictional forces on existing cannula seals. Therefore,the combined effect of all parasitic insertion forces on instrument 110between a shaft face 152 and cannula seal 302 may be greater than thetransverse force transducer sensitivity. It may be possible to improvethe transverse force sensitivity further in the future, resulting in aneed for a similar improvement in the force sensitivity in the axialdirection. Greased seals in combination with present seal designs cannotaccomplish the sensitivity needed to provide for reliable force feedbackto the surgeon.

Experimental coating of existing molded silicone rubber seals with a drylubricant parylene managed to reduce the friction between the shaft andthe seal by a factor of approximately 4 as opposed to the uncoated seal.The force can be measured with a handheld force gauge. However, theasymmetric nature of the friction caused by conventional seal lipscauses a difference in the friction depending on the direction of motionof the shaft through the seal. This asymmetric nature detrimentallyaffects the ability of the force applied at the effector to bedetermined by the surgeon.

In particular, in order to provide for a highly reliable indication ofthe force along shaft 152, both in insertion and retraction, it isdesirable that the frictional force between cannula seal 302 attached tocannula seal mount 212 be as symmetric as possible with respect todirection of motion and as uniform as possible during motion. In thatcase, an estimate of the frictional force can be subtracted from theinsertion direction forces measured by a sensor. It is also desirablethat the frictional force be as low as possible in order to minimize anyremaining error in the improved estimate of the insertion directionsurgical force on patient tissue obtained by subtracting the estimatedfriction force from the sensor measured force.

Friction between instrument shaft 152 and cannula seal 302 are a majorsource of force noise for force sensors 304 trying to sense forceapplied at end effector 206 from outside the body. This is especiallytrue for force sensors 304 that sense forces along the insertion axis ofinstrument shaft 152.

The friction between instrument shaft 152 and cannula seal 302 can bemodeled with a variety of models. FIG. 5A shows graphs illustrating fourof those models. Graph 502 shows force versus velocity in a model ofCoulomb friction. Graph 504 shows force versus velocity in a model thatcombines Coulomb and viscous factors. Graph 506 shows force versusvelocity in a model that combines Static friction, Coulomb friction, andviscous friction. Graph 508 shows force versus velocity in a Stribeckmodel. FIG. 5B illustrates the force versus time in a model thatcombines Static friction, Coulomb friction, and viscous friction. Asshown in FIG. 5B, the force increases during a static period 510 untilmovement is started at point 512, after which a constant force canprovide for sliding in period 514. Static period 510 can vary and can bedifficult to precisely model.

The modeled force can be subtracted from the force readings from forcesensor 304 in step 312. However, the problem with modeling the staticperiod 510 is that the friction force can vary greatly with no resultingmovement of the system. Therefore, it is difficult to correctly predictwhich point along the curve illustrated in FIG. 5B is correct for agiven force and position. Additionally, friction models can vary asparts wear and if fluids are applied between the surfaces (e.g. blood,saline, or other fluids) or the fluids vary over time.

Embodiments of the present invention include a dynamically actuatedcannula seal 302 such that the model utilized can be in the slidingperiod 514 shown in FIG. 5B. The interaction friction between cannulaseal 302 and instrument shaft 152 is therefore that of kinetic (dynamic)friction, which eliminates any static friction (or stiction) betweenseal 302 and instrument shaft 152. In almost all materials, thecoefficient of kinetic friction is lower than that of static friction.Therefore, the frictional force from such a dynamic interaction is lowerthan static friction force at point 512 (just before movement).Additionally, the dynamic force as shown in period 514 of FIG. 5B ismore uniform, accurate, and predictable. Therefore, the model used fordetermining the friction between seal 302 and instrument shaft 152 sothat it can be subtracted from the measured force in step 312 is moreuniform, accurate, and predictable as well.

FIGS. 6A and 6B illustrate an embodiment of a seal 302 and actuator 600that continuously rotates seal 302 on instrument shaft 152. As shown inFIG. 6A, actuator 600 includes a motor 602 that drives a pulley 604. Adrive belt 606 couples pulley 604 with shaft seal 302. In some cases,actuator 600 may rotate seal 302 without rotating any part of cannula202. In some embodiments, shaft seal 302 may be mounted on a cannulapart that rotates with shaft seal 302.

In some embodiments, motor 602 of actuator 600 can be an electric motoror a pneumatic motor or a piezo motor. In FIG. 6A, motor 602 is shownwith pulley 604 and drive belt 606. In same embodiments, motor 602 maybe mechanically coupled rotate seal 302 with a gear drive or other drivemechanism. In some embodiments, for example, actuator 600 can include agear that engages a gear connected to seal 302, as shown in FIG. 6C, ora gear connected to a rotatable portion of cannula 202 to rotate seal302.

If motor 602 is a pneumatic motor, motor 602 can utilize the pressuredifference between the insufflated inner lumen and the patient'sexterior to drive pulley 604. A pneumatically driven motor can also bedriven by an external pressure source.

FIG. 6B illustrates further parts of actuator 600 and seal 302. As shownin FIG. 6B, seal 302 is rotated around shaft 150. Cannula 202 is held injaws 610 that engage cannula 202 at adaptor 612. Seal 302 is attached toadaptor 612. In some embodiments, adaptor 612 is rotatable on cannula202 and jaws 610 can include a motor that directly drives adaptor 612,which rotates seal 302.

FIG. 7A illustrates another embodiment of seal 302. As shown in FIG. 7A,seal 302 is attached to seal mount 212. Seal 302 includes a body 702, anintegrally formed retaining portion 704, and an integrally formed sealportion 706. As shown in FIG. 7A, retaining portion 704 engages withseal mount 212 of cannula 202 to hold seal body 702 in place. Sealportion 706 extends from seal body 702 to surround an instrument shaftthat is inserted through cannula 202. As is further shown in FIG. 7A,seal portion 706 is coupled to a piezoelectric actuator 708. Actuator708 can vibrate or oscillate the material of seal 706 or an instrumentshaft. Actuator 708 can, for example, be a piezopolymer, that vibratesseal portion 706 to reduce or substantially eliminate static frictionbetween cannula seal 302 and instrument shaft 152. For example, as shownin FIG. 7A, actuator 708 of seal portion 706 can be formed of apiezopolymer such as Polyvinylidene fluoride (PVDF), for example.Actuator 708 can be formed anywhere within seal portion 706 so a sealingmaterial that contacts an inserted surgical instrument shaft 152 can beactuated. In either case, the piezopolymer vibrates seal portion 706 toprevent static contact with instrument shaft 152, eliminating staticfriction. As shown in FIG. 7, wiring 710 can be embedded within body 702of seal 302 and used to electrically drive actuator 708.

FIG. 7B illustrates an embodiment of actuated seal 302 that is driven bya voice coil actuator 714 that can vibrate sealing portion 706 (forexample axially) and maintain transient slipping contact with theinstrument shaft. As shown in FIG. 7B, electrical connections 712 tovoice coil actuator 714 can be embedded within body 702 of seal 302.Alternatively, voice coil actuator 714 can be independent of seal 302and inserted into cannula 202 prior to seal 302 such that seal 302contacts voice coil actuator 714. In which case, electrical connections712 can be directed through the side of cannula 202. In someembodiments, voice coil actuator 714 can include two voice coilspositioned on either side of sealing portion 706. In some embodiments,the two voice coils can be driven oppositely to one another such thatsealing portion 706 is symmetrically under expansion or contraction.

FIGS. 8A, 8B, and 8C illustrate some example embodiments of actuator 708as illustrated in FIG. 7. In the embodiment illustrated in FIG. 8A,actuator 708 includes a ring-shaped piezoelectric material 804. Asdiscussed above, piezoelectric material can be a piezopolymer such asPVDF. As shown in FIG. 8A, electrodes 802 are arranged around theoutside diameter of piezoelectric material 804. The inside diameter ofpiezoelectric material 804 can be lined with a sealing material 806.Sealing material 806 can be a lower friction material. Actuator 708 issized so that the shaft of a surgical instrument is in close sliding oractual contact with sealing material 806. Electrodes 802 can be coupledto a driver 808 with wires 710. Wires 710 can be embedded in body 702and extend from seal 302, as is illustrated in FIG. 7. Wires 710 arecoupled to a driver 808, which electrically drives electrodes 802.Driver 808 can produce an oscillating voltage, for example a square wavevoltage. The driving voltage can be of a strength and frequency toprovide for continuous motion of material 806 against instrument shaft152 with high enough frequency that the vibration is undetectable to thesurgeon (e.g., above about 1 kHz) or does not interfere with thesurgeon's sense of touch.

Electrodes 802 in the example illustrated in FIG. 8A are separated solidrings. As a result, voltage applied to electrodes 802 result in axialexpansion and contraction (i.e. along the long axis of an instrumentshaft inserted through actuator 708) of actuator 802. The drivingvoltage from driver 808 can be of a strength and frequency to providefor continuous motion of material 806 against instrument shaft 152.

Further, in some embodiments the driving frequency can be high enough toprevent interference with other sensors in the surgical environment. Insome embodiments, the force data from sensor 304 can be filtered toremove signals at the driving frequency to remove any influence of theactuation from the force data. In either case, the vibrations caused bydriving the piezoelectric material do not result in haptic feedback tothe operator in step 314 of FIG. 3B or feedback to the patient sidemanipulator in 317.

Electrodes 802 in the example illustrated in FIG. 8B are partiallyinterdigitated. This may reduce the axial motion of actuator 708, butintroduces an expansion and contraction motion. In this embodiment, thegrip between material 806 and an instrument shaft 152 and the axiallocation of material 806 with respect to instrument shaft is periodic.The result is that material 806 is in constant motion with respect toinstrument shaft 152.

Electrodes 802 in the example of actuator 708 illustrated in FIG. 8C areinterdigitated more fully than the example illustrated in FIG. 8B. As aresult, the axial motion of actuator 708 can be greatly reduced and theexpansion and contraction of actuator 708 can be the primary motion.This results in a periodicity in the contact between material 806 andinstrument shaft 152. In some embodiments, contact between instrumentshaft 152 and material 806 can be periodically broken. This motion willprevent material 806 from exhibiting static friction against instrumentshaft 152. The additional axial motion can further prevent any remainingstatic friction between material 806 and instrument shaft 152.

FIG. 8C also illustrates that material 806 can include ridges 810.Material 806 in the examples illustrated in FIGS. 8A and 8B may alsoinclude ridges 810. Ridges 810 can provide a seal against instrumentshaft 152 while reducing the contact area between material 810 andinstrument shaft 152.

FIGS. 9A and 9B illustrate an embodiment of seal 302 that utilizes apressure driven actuator. In the embodiment of seal 302 illustrated inFIG. 9A, sealing portion 706 includes a cavity 902. The pressure withincavity 902 can be modulated through passageway 904. FIG. 9B illustratesthe interaction between sealing portion 706 and instrument shaft 152. Asshown in FIG. 9B, sealing portion 706 engages instrument shaft 152 whencavity 902 is pressurized. In some embodiments, cavity 902 may notengage instrument shaft 152 when it is unpressurized. Pulse source 906can provide pressure pulses through passageway 904 to cavity 902 suchthat sealing portion 706 periodically engages instrument shaft 152.Consequently, the material of sealing portion 706 is in motion relativeto instrument shaft 152 reducing the static friction between sealingportion 706 and instrument shaft 152.

The pressure pulses can be of low frequency or high frequency. Asdiscussed above, high frequency pulses can be filtered from the forcedata generated by sensor 304 so that a surgeon operating the instrumentdoes not feel that vibration. In some cases, the frequency can be ashigh as, for example, 1 kHz, and may be generated as an audible tonetransmitted through passageway 904. Furthermore, the amplitude of thepulse, which correlates with the size of the vibration imparted tosealing portion 706 from chamber 902, may not be large. It is sufficientthat sealing portion 706 be actuated where sealing portion 706 contactsinstrument shaft 152 so that sealing portion 706 is in motion resultingin a reduction of the static friction between sealing portion 706 andinstrument shaft 152.

As discussed above, embodiments of seal 302 can be actuated in aconstant, oscillatory, or intermittent motion. The actuation motion mayresult in rotary, axial, or diametric motions. Axial motion may bedivided between opposite motions of two annular portions of sealingportion 706 of seal 302 that contact the surface instrument shaft 152 sothat there is no net axial force applied to instrument shaft 152. Insome embodiments, sealing portion 706 of seal 302 is rotated or vibratedonly as the instrument shaft's velocity along the insertion axis of theinstrument is below a threshold value close to zero (0). If the motionof seal 302 is not constant relative to the instrument shaft, thedriving frequency of seal 302 may be high enough to not affect thecontrol system of the manipulator that controls any instrument in thesurgical area and further may be high enough to be above the sensedfrequency of any sensors within the surgical area. In some cases,filtering may be used to remove noise artifacts in force sensor 304 orother sensors in the area that may be due to a vibratory excitation ofcannula seal 302.

The above detailed description is provided to illustrate specificembodiments of the present invention and is not intended to be limiting.Numerous variations and modifications within the scope of the presentinvention are possible. The present invention is set forth in thefollowing claims.

What is claimed is:
 1. A surgical system, comprising: means forcontrolling a surgical instrument, the surgical instrument comprising aninstrument shaft; means for receiving the instrument shaft, the meansfor receiving comprising means for sealing against the instrument shaft,the means for sealing being sized and shaped to slidably engage theinstrument shaft; and means for causing continuous, oscillatory, orintermittent rotational motion of the means for sealing relative to theinstrument shaft.
 2. The surgical system of claim 1, wherein the meansfor causing continuous, oscillatory, or intermittent rotational motioncomprises a motor that rotates the means for sealing relative to theinstrument shaft.
 3. The surgical system of claim 2, wherein the motoris an electric motor.
 4. The surgical system of claim 2, wherein themotor is a pneumatic motor.
 5. The surgical system of claim 4, whereinthe pneumatic motor is driven by insufflation pressure.
 6. The surgicalsystem of claim 2, wherein: the means for sealing is a cannula seal; thecannula seal comprises a base portion that engages with the means forreceiving and a seal portion coupled to the base portion; the motor iscoupled to the base portion of the cannula seal with a drive belt; androtation of the base portion induces rotation of the seal portionrelative to the instrument shaft.
 7. The surgical system of claim 2,wherein: the means for sealing is a cannula seal: the cannula sealcomprises a base portion that engages with the means for receiving and aseal portion coupled to the base portion, the motor is coupled to thebase portion of the cannula seal through a gear; and rotation of thebase portion induces rotation of the seal portion relative to theinstrument shaft.
 8. The surgical system of claim 1, wherein the meansfor causing continuous, oscillatory, or intermittent rotational motioncomprises a piezoelectric actuator.
 9. The surgical system of claim 8,wherein the piezoelectric actuator comprises a piezopolymer.
 10. Thesurgical system of claim 8, wherein the piezoelectric actuator is in aring integrated with the means for sealing.
 11. The surgical system ofclaim 10, wherein the piezoelectric actuator comprises electrodesarranged around an outside diameter of the ring.
 12. The surgical systemof claim 11, wherein the electrodes comprise separated rings arrangedaround the outside diameter of the ring.
 13. The surgical system ofclaim 11, wherein the electrodes comprise separated and partiallyinterdigitated electrodes.
 14. The surgical system of claim 11, whereinthe electrodes comprise interdigitated electrodes.
 15. The surgicalsystem of claim 11, wherein the electrodes are driven at a frequencyhigh enough not to interfere with a surgeon's sense of touch.
 16. Thesurgical system of claim 1, wherein the means for causing continuous,oscillatory, or intermittent rotational motion comprises at least onevoice coil in contact with the means for sealing.
 17. The surgicalsystem of claim 16, wherein the means for causing continuous,oscillatory, or intermittent rotational motion includes two voice coilson either side of the means for sealing, the two voice coils beingdriven oppositely to one another.
 18. The surgical system of claim 16,wherein the at least one voice coil is driven at a frequency high enoughto not interfere with a surgeon's sense of touch.
 19. The surgicalsystem of claim 1, wherein the means for causing continuous,oscillatory, or intermittent rotational motion is configured topneumatically pulse a cavity defined at least in part by the means forsealing.
 20. The surgical system of claim 19, wherein the means forcausing continuous, oscillatory, or intermittent rotational motionpneumatically pulses at a pulse frequency that is high enough to notinterfere with a surgeon's sense of touch.